2. Human Digestion

3. Nutrition Process by which organisms obtain and utilize their food. There are two parts to Nutrition: 1. Ingestion- process of taking food into the digestive system so that it may be hydrolized or digested. 2. Digestion- the breakdown of food (either chemically or mechanically) in order to utilize nutrients

4. Types of Nutrients Micronutrients- vitamins, minerals, & water Macronutrients- proteins, lipids, carbohydrates, etc…

5. Human digestive system

6. GI (gastrointestinal) tract = alimentary canal

7. Ingestion Mouth –mechanical digestion teeth –breaking up food –chemical digestion saliva –amylase »enzyme digests starch –mucin »slippery protein (mucus) »protects soft lining of digestive system »lubricates food for easier swallowing –buffers »neutralizes acid to prevent tooth decay –anti-bacterial chemicals »kill bacteria that enter mouth with food

8. mouth  break up food  digest starch  kill germs  moisten food

9. Mouth Chemical and mechanical digestion. Food is chewed (masticated) mechanically. A bolus (lump) is formed with saliva and the tongue.

10. Swallowing (& not choking) Epiglottis –flap of cartilage –closes trachea (windpipe) when swallowing –food travels down esophagus Peristalsis –involuntary muscle contractions to move food along

11. Which type of digestion is the following? 1.Chewing a saltine? - 2. Saliva breaking the saltine down into molecules of glucose? - 3. Your tongue breaking pieces of a hamburger apart? 4. Pepsin (an enzyme) in your stomach breaking the hamburger into amino acids?

12. Pharynx The back of the throat. Larynx- passage for air, closes when we swallow. Is approximately 15cm long.

13. Digestive Glands Groups of specialized secretory cells. Found in the lining of the alimentary canal or accessory organs.

14. series of involuntary wave-like muscle contractions which move food along the digestive tract Peristalsis

15. Stomach Food is temporarily stored here. Gastric juices are secreted. Has layers of muscle that line the inside. Mechanically and chemically breaks down food.

16. Stomach Functions –food storage can stretch to fit ~2L food –disinfect food HCl = pH 2 –kills bacteria –chemical digestion pepsin –enzyme breaks down proteins But the stomach is made out of protein! What stops the stomach from digesting itself? mucus secreted by stomach cells protects stomach lining

17. stomach  kills germs  break up food  digest proteins  store food sphincter mouth  break up food  digest starch  kill germs  moisten food

18. Gastric Juices Secreted by the stomach. Acidic (pH 1.5-2.5) (HCl). Pepsin- an enzyme that breaks down large proteins into amino acids. Food is further broken down into a thin liquid called chyme.

20. Accessory Organs Pancreas Gall Bladder Spleen

21. Gall bladder Pouch structure located near the liver which concentrates and stores bile Bile duct – a long tube that carries BILE. The top half of the common bile duct is associated with the liver, while the bottom half of the common bile duct is associated with the pancreas, through which it passes on its way to the intestine.

22. BILE Bile emulsifies lipids (physically breaks apart FATS) Bile is a bitter, greenish-yellow alkaline fluid, stored in the gallbladder between meals and upon eating is discharged into the duodenum where it aids the process of digestion.

23. Pancreas An organ which secretes both digestive enzymes (exocrine) and hormones (endocrine) ** Pancreatic juice digests all major nutrient types. Nearly all digestion occurs in the small intestine & all digestion is completed in the SI.

24. Pancreas Digestive enzymes –digest proteins trypsin, chymotrypsin –digest starch amylase Buffers –neutralizes acid from stomach

26. Liver Function –produces bile bile stored in gallbladder until needed breaks up fats –act like detergents to breakup fats bile contains colors from old red blood cells collected in liver = iron in RBC rusts & makes feces brown bile contains colors from old red blood cells collected in liver = iron in RBC rusts & makes feces brown

27. pancreas  produces enzymes to digest proteins & starch stomach  kills germs  break up food  digest proteins  store food mouth  break up food  digest starch  kill germs  moisten food liver  produces bile - stored in gall bladder  break up fats

28. Small Intestine Most chemical digestion takes place here. Simple sugars and proteins are absorbed into the inner lining. Fatty acids and glycerol go to lymphatic system. Lined with villi, which increase surface area for absorption, one cell thick.

29. Small intestine Function –chemical digestion major organ of digestion & absorption –absorption through lining over 6 meters! small intestine has huge surface area = 300m 2 (~size of tennis court) Structure –3 sections duodenum = most digestion jejunum = absorption of nutrients & water ileum = absorption of nutrients & water

30. Duodenum 1st section of small intestines –acid food from stomach –mixes with digestive juices from:  pancreas  liver  gall bladder

31. stomach  kills germs  break up food  digest proteins  store food mouth  break up food  digest starch  kill germs  moisten food pancreas  produces enzymes to digest proteins & starch

32. Absorption in the SI Much absorption is thought to occur directly through the wall without the need for special adaptations Almost 90% of our daily fluid intake is absorbed in the small intestine. Villi - increase the surface area of the small intestines, thus providing better absorption of materials

33. Absorption by Small Intestines Absorption through villi & microvilli –finger-like projections –increase surface area for absorption

34. VILLI

35. Large intestines (colon) Function –re-absorb water use ~9 liters of water every day in digestive juices > 90% of water reabsorbed –not enough water absorbed »diarrhea –too much water absorbed »constipation

36. Large Intestine Solid materials pass through the large intestine. These are undigestible solids (fibers). Water is absorbed. Vitamins K and B are reabsorbed with the water. Rectum- solid wastes exit the body.

37. You’ve got company! Living in the large intestine is a community of helpful bacteria –Escherichia coli (E. coli) produce vitamins –vitamin K; B vitamins generate gases –by-product of bacterial metabolism –methane, hydrogen sulfide

38. Appendix Vestigial organ

39. Rectum Last section of colon (large intestines) –eliminate feces undigested materials –extracellular waste »mainly cellulose from plants »roughage or fiber –masses of bacteria

40. Digestive Homeostasis Disorders ULCERS – erosion of the surface of the alimentary canal generally associated with some kind of irritant

41. CONSTIPATIONCONSTIPATION – a condition in which the large intestine is emptied with difficulty. Too much water is reabsorbed and the solid waste hardens Digestive Homeostasis Disorders

42. DIARRHEA – a gastrointestinal disturbance characterized by decreased water absorption and increased peristaltic activity of the large intestine. This results in increased, multiple, watery feces. This condition may result in severe dehydration, especially in infants

43. Digestive Homeostasis Disorders APPENDICITIS – an inflammation of the appendix due to infection Common treatment is removal of the appendix via surgery

44. Digestive Homeostasis Disorders GALLSTONES – an accumulation of hardened cholesterol and/or calcium deposits in the gallbladder Can either be “passed” (OUCH!!) or surgically removed

45. Digestive Homeostasis Disorders ANOREXIA NERVOSA - a psychological condition where an individual thinks they appear overweight and refuses to eat. Weighs 85% or less than what is developmentally expected for age and height Young girls do not begin to menstruate at the appropriate age.

46. Digestive Homeostasis Disorders HEART BURN – ACID from the stomach backs up into the esophagus.

47. Human Anatomy, 3rd edition Prentice Hall, © 2001 Overview of Digestive System

48. Human Anatomy, 3rd edition Prentice Hall, © 2001 Histological Organization Same basic arrangement of tissues from esophagus to anal canal Four layers (from innermost to outermost) –Mucosa –Submucosa –Muscularis –Serosa

49. Human Anatomy, 3rd edition Prentice Hall, © 2001 Movement and Mixing of Digestive Materials Peristalsis –Coordinated motion of two muscular layers –Circular muscles contract, then longitudinal muscles Segmentation –Mixing of food –Circular muscles in two areas contract –Longitudinal muscles alternately contract & relax

50. Human Anatomy, 3rd edition Prentice Hall, © 2001 External Anatomy of the Stomach

51. Human Anatomy, 3rd edition Prentice Hall, © 2001 The Stomach Same 4 basic layers When the stomach is empty, the mucosa lies in large folds –Rugae Pyloric sphincter separates stomach from small intestine

52. Human Anatomy, 3rd edition Prentice Hall, © 2001 Histology of the Stomach Mucosa is simple columnar epithelium with goblet cells Mucosa is folded to form gastric pits –Gastric glands secrete gastric juice

53. Human Anatomy, 3rd edition Prentice Hall, © 2001 Gastric Gland Several kinds of cells produce substances that form gastric juice –Mucus cells –Chief cells –Parietal cells –Enteroendocri ne cells

54. Human Anatomy, 3rd edition Prentice Hall, © 2001 Functions of the Stomach Mechanical digestion –Food reaches pylorus Chemical digestion –Digestion of proteins Absorption –No food –Water, electrolytes –Some drugs –Alcohol

55. Human Anatomy, 3rd edition Prentice Hall, © 2001 The Small Intestine About 18 feet long The duodenum –About 8 inches long –Common bile duct & pancreatic duct empty here The jejunum –About 8 feet long –Most digestion occurs here The ileum –About 9.5 feet long –Most absorption occurs here –Ends in the ileocecal valve

56. Human Anatomy, 3rd edition Prentice Hall, © 2001 Histology of the Small Intestine The lining is folded into circular pleats –Plicae circulares The mucosal surface is folded into villi The epithelial cell membranes are highly folded into microvilli Intestinal glands are found in the crypts at the base of villi –Secrete intestinal juice

57. Human Anatomy, 3rd edition Prentice Hall, © 2001 A Villus

58. Human Anatomy, 3rd edition Prentice Hall, © 2001 Functions of the Small Intestine Chyme is further broken down –Proteins –Carbohydrates –Fats Most absorption is in the small intestine

59. Human Anatomy, 3rd edition Prentice Hall, © 2001 The Large Intestine (Colon) About 4.5 feet long Mesocolon supports Begins with the cecum Appendix is attached Ascending colon Transverse colon Descending colon Sigmoid colon Colon connects to rectum Rectum connects to anal canal Empties to the exterior through the anus

60. Human Anatomy, 3rd edition Prentice Hall, © 2001 Histology and Functions of the Large Intestine Mucosa - simple columnar epithelium –Completion of absorption –Formation of feces Lots of mucus glands Expulsion of feces from the body

61. Human Anatomy, 3rd edition Prentice Hall, © 2001 The Liver Performs many life- sustaining functions Location – under the diaphragm on the right –Connected to the diaphragm by the falciform ligament Divided into lobes –Right lobe –Left lobe –Caudate lobe –Quadrate lobe

62. Human Anatomy, 3rd edition Prentice Hall, © 2001 Histology of the Liver Outside is a capsule Composed of tiny lobules Each lobule is surrounded by liver cells and sinusoids –Hepatocytes –Kupffer cells Bile ducts run between liver cells

63. Human Anatomy, 3rd edition Prentice Hall, © 2001 The Gallbladder Location – underside of right lobe of liver Function – concentrate and store bile –Collected from liver Hepatic ducts –Adds bile to duodenum Cystic duct Common bile duct Gallstones

64. Human Anatomy, 3rd edition Prentice Hall, © 2001 The Pancreas Location – in the curvature of the duodenum Connected to the duodenum by the pancreatic duct Produces pancreatic juice Functions –Exocrine - digestion of all nutrient groups –Endocrine – control blood glucose level